Gear mechanism and a rotary encoder equipped with this gear mechanism

ABSTRACT

A gear mechanism includes a rotating input element, a rotating output element, and at least one first force transmission device arranged along a spiral line on a face of the input element. A second force transmission device is arranged along an encircling line on a face of the output element. The interaction of these force transmission devices transmits a turning moment from the input element to the output element, whereby this turning moment effects a rotating motion in the output element so that the rotational speed is lower than the rotational speed of the input element. A rotary encoder may be equipped with a gear mechanism of the aforementioned type.

FIELD OF THE INVENTION

The present invention relates to a gearing and to a rotary encoderequipped with such gearing.

BACKGROUND INFORMATION

In addition to angle-measuring instruments, which allow an anglemeasurement at a rotatable shaft in incrementable measuring steps,so-called absolute angle-measuring instruments—also referred to asrotary encoders—are conventional as well. These allow an absolute angledetermination within a single shaft rotation. Furthermore, if the numberof performed shaft rotations is to be recorded as well, so-calledmultiturn rotary encoders are generally utilized. With such multiturnrotary encoders, the absolute angular position is determined within oneshaft rotation, i.e., between 0° and 360°, via a code disk connected tothe shaft, which is scanned with the aid of a suitable photoelectricscanning unit. To obtain the required information regarding the numberof effected shaft rotations, a reduction or step-down gear is typicallyprovided, via which one or more additional graduated disks or code disksis/are set into a rotary motion having a low number of revolutions perunit of time, while the shaft is rotating. These code disks are oftendesigned as magnetized disks, each having at least one north-pole andone south-pole sector. The rotational position of these additional codedisks is normally recorded in a conventional manner with the aid ofsuitable scanning units, in particular Hall sensors. Due to thespecified reduction of the rotary motion of the additional code disks,it is possible to ascertain the number of effected rotations of theshaft in this manner. A measurement of the absolute position of thedriven shaft may thus be carried out also over a plurality of rotations.

It may be advantageous in such reduction gearings if the first reductionstep utilizes the highest possible reduction ratio so that the gearwheels of the subsequent gearing steps rotate at an already considerablylower rotational frequency. This significantly reduces the loading ofthe subsequent gear steps.

A similarly configured multiturn rotary encoder is described in GermanPublished Patent Application No. 198 20 014, of the applicant hereof.This describes an integrated construction method for electroniccomponents of rotary encoders.

German Published Patent Application No. 197 45 177 describes a gearingsystem in which permanently magnetic or ferromagnetic, spiral-shapedsegments are arranged along the peripheral areas of a drive gear and anoutput gear. This design may be disadvantageous insofar as it requiresrelatively large installation space, in particular as far as the outerdimensions in the radial direction are concerned.

The demand for rotary encoders having smaller structural dimensionscontinues to grow. Since the electronic components of rotary encodersare integrated to an ever greater extent and are thus miniaturized aswell, the installation space for the mechanical components of thesedevices often becomes a limiting factor in such miniaturizationendeavors.

SUMMARY

An example embodiment of the present invention may provide a gearingthat has small structural dimensions and may be produced at low cost.

The gearing may be used in a rotary encoder.

In an example embodiment of the present invention, a very high reductionratio may be achieved by the gearing, and the outer diameter of theentire rotary encoder may be kept small at the same time. Furthermore,the installation space required in the axial direction may becomparatively low. In addition, the gearing according to an exampleembodiment of the present invention may have a relatively low massinertia, which may be advantageous especially with high dynamic changesin rotary motions.

In the following text, the end face of the drive or output elementshould be understood as an area that is substantially perpendicular toits axis of rotation. In a circular-cylindrical drive or output element,the end face should thus not be understood as the lateral surface but asone of the circular or ring surfaces.

The force-transmission arrangement of the gearing may be configured aspermanent magnets. The permanent magnets are arranged on the drive gearalong a spiral line and the permanent magnets on the output element arearranged along a circular curve, for instance. The action of the gearingmay be improved if the spiral line on the drive element is configured aspart of an Archimedean spiral. To increase the magnetic forces, thebodies of the drive gear and the output gear to which the permanentmagnets are affixed may be made of a material having high relativepermeability, which, as a minimum, exceeds the value 10 and is greaterthan 100, for example.

According to an example embodiment of the present invention, a gearingincludes: a rotatable drive element; a rotatable output element; atleast one first force-transmission device arranged at an end face of thedrive element along at least one spiral line; and a secondforce-transmission device arranged at an end face of the output elementalong a circumferential line. In accordance with reciprocal action ofthe first force-transmission device and the second force-transmissiondevice, the first force-transmission device and the secondforce-transmission device are configured to transmit torque from thedrive element to the output element to effect a rotary motion in theoutput element. A frequency of rotation of the output element is lowerthan a frequency of rotation of the drive element.

According to an example embodiment of the present invention, a rotaryencoder includes at least one gear step. Each gear step includes: arotatable drive element; a rotatable output element; at least one firstforce-transmission device arranged at an end face of the drive elementalong at least one spiral line; and a second force-transmission devicearranged at an end face of the output element along a circumferentialline. In accordance with reciprocal action of the firstforce-transmission device and the second force-transmission device, thefirst transmission device and the second transmission device areconfigured to transmit torque from the drive element to the outputelement to effect a rotary motion in the output element, and a frequencyof rotation of the output element is lower than a frequency of rotationof the drive element.

According to an example embodiment of the present invention, a gearingincludes: rotatable drive means; rotatable output means; at least onefirst force-transmission means arranged at an end face of the drivemeans along at least one spiral line; and second force-transmissionmeans arranged at an end face of the output means along acircumferential line. In accordance with reciprocal action of the firstforce-transmission means and the second force-transmission means, thefirst force-transmission means and the second force-transmission meanstransmit torque from the drive means to the output means to effect arotary motion in the output means, and a frequency of rotation of theoutput means is lower than a frequency of rotation of the drive means.

According to an example embodiment of the present invention, a rotaryencoder includes at least one gear step. Each gear step includes: arotatable drive means; a rotatable output means; at least one firstforce-transmission means arranged at an end face of the drive meansalong at least one spiral line; and a second force-transmission meansarranged at an end face of the output means along a circumferentialline. In accordance with reciprocal action of the firstforce-transmission means and the second force-transmission means, thefirst force-transmission means and the second force-transmission meanstransmit torque from the drive means to the output means to effect arotary motion in the output means, and a frequency of rotation of theoutput means is lower than a frequency of rotation of the drive means.

Further details and aspects of the gearing and a rotary encoder providedtherewith are set forth in the following description of exemplaryembodiments with reference to the appended Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a plan view of the drive gear having permanent magnets.

FIG. 1 b is a side view with a partial section of the drive gear havingpermanent magnets.

FIG. 1 c is a perspective view of the drive gear.

FIG. 2 a is a plan view of the output gear with permanent magnets anddriving pins.

FIG. 2 b is a side view including a partial section of the output gearwith permanent magnets and driving pins.

FIG. 2 c is a perspective view of the output gear with permanent magnetsand driving pins.

FIG. 2 d is a plan view of the output gear with driving pins arrangedinside the permanent magnets.

FIG. 2 e is a side view including a partial section of the output gearwith driving pins arranged inside the permanent magnets.

FIG. 3 a is a side view of the drive gear and the output gear in theoperating position.

FIG. 3 b is a perspective view of the gearing with permanent magnets andtilted output axle as well as driving pins.

FIG. 3 c a side view with a partial section of the drive gear withpermanent magnets having different bar height, and with partial outputgear.

FIG. 3 d is a partial view of the gearing having permanent magnetsmagnetized in the circumferential direction.

FIG. 3 e is a partial view of the gearing with permanent magnetsmagnetized in the circumferential direction, in combination withpermanent magnets magnetized in the radial direction.

FIG. 4 is a perspective exploded view of the output gear with permanentmagnets and shielding plate.

FIG. 5 a is a plan view of the drive gear having grooves.

FIG. 5 b is a side view with a partial section of the drive gear havinggrooves.

FIG. 6 a is a plan view of the drive gear with balls in a ball cage.

FIG. 6 b is a side view with a partial section of the drive gear withballs in a ball cage.

FIG. 6 c is a perspective exploded view of the output gear with a ballcage and balls.

FIG. 7 is a spatial exploded representation of a rotary encoder withpartial sections.

DETAILED DESCRIPTION

Equally acting components of different exemplary embodiments areprovided with identical reference signs in the Figures.

FIG. 1 a is a plan view of drive gear 100 of the gearing according to anexample embodiment of the present invention as it is installed as firstgear step in a rotary encoder 400 (FIG. 7). Drive gear 100 has a largecentral bore to accommodate a hollow shaft 401 (shown in FIG. 7), therotational position of which is measured during operation of rotaryencoder 400. At a front end of drive gear 100, aligned along a spiralcurve in each case, are two longitudinal permanent magnets 101, 102(FIG. 1 b), which are arranged at a 180° offset, arranged on top is aspiral-shaped plate 104, the edges of which extend according to the formof permanent magnets 101, 102. Plate 104 is bonded to permanent magnets101, 102. Plate 104 is made of a ferromagnetic alloy, so that themagnetic field of permanent magnets 101, 102 is intensified. Body 106 ofdrive gear 100 is made of a ferromagnetic FeNi alloy, which has arelative permeability μ_(r) of at least 10, and, e.g., of 1000. In theexample illustrated, μ_(r) is approximately 3000.

In this exemplary embodiment, the spiral curve is configured as part ofan Archimedean spiral according to the equation r=a·φ, r representingthe radius of the spiral and a representing a constant positive number.φ should be understood to represent the pivoting angle (in radians) of aradial beam about the pole of the spiral curve. Since the spiral in theillustrated example is centrically arranged with respect to drive gear100, the pole is located on axis of rotation 103. In this type ofspiral, two consecutive intersections of an arbitrary beam originatingfrom the pole of the spiral have the same spacing, namely 2·φ·a.

Permanent magnets 101, 102 and plate 104 are of different thickness inthe radial direction, the thinnest regions being at the beginning andthe end of permanent magnets 101, 102 or plate 104.

As illustrated in FIG. 1 b, permanent magnets 101, 102 are magnetized inthe axial direction with respect to drive gear 100, which means that theconnecting line between north pole and south pole of a permanent magnet101, 102 extends substantially in parallel to axis of rotation 103 ofdrive gear 100. The two spiral-shaped permanent magnets 101, 102 arearranged such that in one permanent magnet 101 the south pole is facingbody 106 of drive gear 100, and in the other permanent magnet 102 it isthe north pole.

FIG. 1 c illustrates drive gear 100 with permanent magnets 101, 102 andplate 104 in a perspective illustration.

As illustrated in FIGS. 2 a, 2 b, and 2 c, output gear 200 also includespermanent magnets 201, 202, which are arranged along a circular line 205at the end face of output gear 200. As an alternative to a circular line205, permanent magnets 201, 202 may also be arranged along an ellipsis,for example.

Permanent magnets 201, 202 may be placed along a circumferential line,which means that a virtual beam, originating from axis of rotation 203and directed radially outwardly, intersects the circumferential line inevery angular position between 0° and 360°. The edge regions of the endfaces of permanent magnets 201, 202 are beveled in a radially outwarddirection with respect to axis of rotation 203, at an angle α, which is50 in this example (FIG. 2 b).

Permanent magnets 201, 202 are bonded to body 206 of output gear 200,which is made of a ferromagnetic FeNi alloy and has a relativepermeability μ_(r) of at least 10 and, e.g., of 1000 as in the case ofdrive gear 100. In the illustrated example, μ_(r) is also approximately3000. This comparatively high relative permeability may significantlyintensify the magnetic field.

Permanent magnets 201, 202 are magnetized in the axial direction(relative to axis of rotation 203 of output gear 200) and aligned suchthat two adjacent permanent magnets 201, 202 exhibit opposingmagnetization in each case. This means that the north pole of permanentmagnet 201 points in the direction of body 206 of output gear 200,whereas it is the south pole in adjacent permanent magnet 202. So-calleddriving pins 204, made of aluminum, are arranged on output gear 200between permanent magnets 201, 202.

As an alternative, driving pins 204, instead of being arranged betweenpermanent magnets 201, 202, may be arranged inside permanent magnets201, 202, rotationally offset by one-half of a pole distance, asillustrated in FIGS. 2 d and 2 e. Driving pins 204 are made of amagnetizable material and magnetized themselves as well, having the samealignment and polarity as permanent magnets 201, 202.

As an alternative to driving pins 204 in the form of separatecomponents, driving pins 204 may be monolithically integrated withinpermanent magnets 201, 202 by appropriate shaping of the permanentmagnets.

FIG. 3 a illustrates drive gear 100 in its operation-appropriateposition relative to output gear 200. During operation, axis of rotation103 of drive gear 100 and also axis of rotation 203 of output gear 200are stationary. Due to the fact that axis of rotation 203 of output gear200 is inclined at an angle α (=50) with respect to axis of rotation 103of drive gear 100, the front-side spacing between drive gear 100 andoutput gear 200 is of different size depending on the location.Consequently, the magnetic forces between permanent magnets 101, 102 ofdrive gear 100 and permanent magnets 201, 202 of output gear 200 are ofdifferent magnitude as well, depending on the clearance or the air gap.Furthermore, driving pins 204 are free in the region of the largeclearance, which means that their ends do not project into the gaps ofspiral-shaped plate 104 in this region.

FIG. 3 b is a perspective partial view of the gearing with drive gear100 and output gear 200 in the operating position.

If drive gear 100 is set in motion, the north pole of permanent magnet201 virtually “catches” the south pole of permanent magnet 201 of outputgear 200 as soon as a sufficiently small air gap or clearance comesabout between the poles of permanent magnets 101, 201 of drive gear 100and output gear 200. In this manner, a force transmission is achievedfrom drive gear 100 to output gear 200. Due to the fact that bodies 106,206 of drive gear 100 and output gear 200 are made of a NiFe alloy,which has a relative permeability μ_(r) of approximately 3000, themagnetic field and thus the transmittable force may be intensified orincreased. Furthermore, this effect may be reinforced by ferromagnetic,e.g., magnetically hard sheet 104, which may lead to a fieldconcentration, which may increase the force yield further. Since therotary motion about axis of rotation 103 of spiral-shaped permanentmagnet 101 has a directional component, which has a tangentialorientation with respect to output gear 200, a torque going out fromdrive gear 100 is introduced into output gear 200. The forcetransmission essentially occurs into the region in which a small air gapprevails. Due to the tilting at angle α, it may be ensured that the sumof all magnetic forces between permanent magnets 101, 201 of drive gear100 and output gear 200 triggers a rotary motion. Since the thickness isuneven in the radial direction of permanent magnet 101 and plate 104 atthe beginning and end of permanent magnet 101, the threading procedureof driving pins 204 into the clearance between the spiral lines may beimproved.

The reduction ratio of the gearing depends on the number of threads ofthe spiral line along which permanent magnet 101 extends, on the onehand, and on the number of permanent magnets 201 of output gear 200 ableto be brought into operative connection therewith, on the other hand. Inthe example illustrated, permanent magnet 101 is aligned along aone-gear spiral line, its north pole pointing to output gear 200. Thenumber of associated south poles or the number of correspondingpermanent magnets 201 of output gear 200 is eight. Since the reductionis the quotient of the number of threads of the spiral line and thenumber of permanent magnets 201 of output gear 200 in reciprocal actionthereto, a reduction of 8:1 results in this case. This means that outputgear 200 rotates eight times more slowly than drive gear 100 duringoperation.

To optimize the force yield and the synchronism of the gearing, the formof the spiral line of permanent magnet 101 is adapted to the arrangementof permanent magnets 201. Since the spiral line along which permanentmagnet 101 is aligned is configured as Archimedean spiral, the constantclearance between the spiral lines is given as 2·π·a as explainedearlier. In the example shown, 2·π·a=4.4 mm, or a=0.7 mm.

The eight permanent magnets 201 of output gear 200 are arranged along acircular curve 205, so that a circular area is able to be formed byextending outer contour 207 of permanent magnets 201. The clearancesbetween permanent magnets 201 are adapted to the variable 2·π·a=4.4 mm,e.g., such that one north pole is “caught” by one south pole in everyoperating position. Expressed in geometrical terms this means that anequilateral octagon having an edge length of 2·π·a=4.4 mm is able to beplaced completely inside the afore-described outer contour 207 of thecircular area. The action function of the gearing may be provided if thefollowing geometrical criterion is satisfied: According to the number nof homopolar permanent magnets 201 of output gear 200, an n-gon havingan edge length of 2·π·a is formed. This n-gon may be placed on thecircular area (each corner onto a permanent magnet 201) such that itcomes to be completely inside outer contour 207 of the circular area.

Analogous relationships with respect to the above statements apply whenthe antipolar operative connection is examined. Accordingly, secondpermanent magnet 102 of drive gear 100 is also arranged along a one-gearspiral line. Its south pole interacts with the eight north poles ofpermanent magnets 202 of output gear 200. The reduction ratio betweenpermanent magnet 102, which is aligned along a one-gear spiral line, andthe eight corresponding permanent magnets 202 of output gear 200 is thus8:1 as well.

This additional operative connection may therefore not result in achange of the reduction ratio with respect to the afore-described forcetransmission between permanent magnets 101 and 201. It may merely serveto increase the force yield or to increase the transmittable torquesince permanent magnets 101 and 102, in interaction with permanentmagnets 201 and 202, work virtually in parallel with one another. Inparticular when the gearing is to be used in rotary encoders, thisparallel method of operation of north-pole and south-pole couplings maybe provided since the danger of an asynchronous operation, i.e.,slippage between drive gear 100 and output gear 200, should be avoidedwithin the meaning of a precise measurement.

Using the gearing as described herein may allow the required torque tobe transmitted without any contact whatsoever. However, to safeguardagainst possible asynchronous, i.e., slip-encumbered, operating states,the non-magnetic driving pins 204 of aluminum are additionally used inoutput gear 200 in the example illustrated. Instead of aluminum, someother non-magnetic material such as brass or bronze, but also a plasticsuch as PTFE or PA, etc., may be used as well. Furthermore, as mentionedearlier, driving pins 204 may be magnetized as well and thus may be madeof a magnetic material. These driving pins 204 are provided to moveoutput gear 200 in a synchronous and non-slip manner with respect todrive gear 100 even if the power coupling via permanent magnets 101,102, 201, 202 should no longer be sufficient to transmit the torque.This danger may arise for example when torque spikes occur in highangular accelerations, but also in the presence of an interferencemagnetic field or when vibrations occur. Plate 104 may ensure that thedriving pins will not contact permanent magnets 101, 102 of drive gear100 since driving pins 204 have such short dimensions that they do notreach permanent magnets 101, 102. In the event that the occurring torqueis so great that driving pins 204 come to have an effect, the contactingforce transmission occurs between driving pins 204 and plate 104.Possible wear of permanent magnets 101, 102 may be avoided in thismanner.

As mentioned previously already, driving pins 204 are magnetized in theexemplary embodiment illustrated in FIG. 2 e. In this case, a torque mayalready be transmitted even without contact or at reduced contactpressure at plate 104 or at permanent magnets 101, 102.

Furthermore, wear of a gearing according to the described example may benegligible since a contactless force transmission takes place duringnormal operation.

As an alternative to the described exemplary embodiment, plate 104 mayalso be omitted. In this case, the edges of permanent magnets 101, 102of drive gear 100 may be provided with a hard material layer, orcomposites may be used.

FIG. 3 c illustrates another exemplary embodiment, which isdistinguished in that permanent magnets 101, 102 have different barheights H, h. In this case, permanent magnets 201, 202 engage betweenpermanent magnets 101, 102 without making contact with the magnetsduring normal operation of the gearing. A corresponding force istransmitted by the attractive and repulsive forces of permanent magnets101, 102 of drive gear 100 and permanent magnets 201, 202 of output gear200. In the event that the gearing is subjected to excessive stress, aforce is mechanically transmitted via contact with permanent magnets101, 102, 201, 202. To reduce wear for this emergency operation,appropriate hard material coatings are provided here. This function isalso aided by the conical shape of permanent magnets 201, 202 of outputgear 200.

Other geometric forms, which deviate from a cylindrical form, may alsobe selected for driving pins 204 of the other exemplary embodiments, forexample, to improve the emergency-running properties.

FIG. 3 d illustrates an additional exemplary embodiment of the gearingin which permanent magnets 101, 102 are magnetized in the radialdirection and permanent magnets 201, 202 are magnetized in thecircumferential direction. Accordingly, in each case four magnetic polesare arranged opposite each other per permanent magnet 101, 102, 201, 202in the gearing. In the case of a relative displacement between permanentmagnets 101, 102 of drive gear 100 and permanent magnets 201, 202 ofoutput gear 200 as a result of the torque to be transmitted, themagnetic forces of the poles will counteract this displacement, therebyresulting in a relatively stiff power-transmission characteristic of thegearing.

In an additional example embodiment of the gearing, permanent magnets101, 102 illustrated in FIG. 3 e may be magnetized in the radialdirection, as in the previous exemplary embodiment, but such that polesof the same type are arranged opposite one another. In the exampleillustrated, the north pole of permanent magnet 101 is arranged acrossfrom the north pole of permanent magnet 102. In contrast, permanentmagnets 201, 202 of output gear 200 are magnetized in the axialdirection. Furthermore, analogously to FIG. 2 e, driving pins 204 aremagnetized as well, e.g., such that the north pole of a driving pin 204projects between the two north poles of permanent magnets 101, 102 ofdrive gear 100. During operation, the south pole of permanent magnet 202of output gear 200 is thus attracted by the two north poles of permanentmagnets 101, 102, so that the system strives for the shortest distancebetween the poles having different polarization. This function is aidedby the repelling forces between the north pole of driving pin 204 andthe north poles of permanent magnets 101, 102. In this arrangement,driving pins 204 may thus contribute to the centering of output gear 200relative to permanent magnets 101, 102 of drive gear 100 and mayultimately lead to an increase in the torque transmittable in acontactless manner.

FIG. 4 illustrates an additional exemplary embodiment in which the forcetransmission is performed via permanent magnets 101, 102, 201, 202.However, in this case an arrangement is selected in which axes ofrotation 103, 203 of drive gear 100 and output gear 200 are aligned inparallel. This may be advantageous, for example, for the subsequent gearsteps since it may allow the axes of all gear wheels to be aligned inparallel with respect to axis of rotation 103, so that no bevel-gearstep or similar device may need to be used.

The parallel alignment of axes of rotation 103, 203 may be made possibleby a screening plate 300 into which a window 301 is introduced.Screening plate 300 is also made of a NiFe alloy having comparativelyhigh relative permeability, which has the property of significantlyweakening magnetic fields. As an alternative, it is also possible toutilize an SiFe alloy or amorphous or nanocrystalline alloys, etc.,having high relative permeability. In this manner, the magnetic couplingbetween drive gear 100 and output gear 200 may spatially be limited tothe area of window 301. The remaining area of output gear 200 ismagnetically insulated to a large extent by screening plate 300, so thatthe transmittable torque is virtually zero in this region.

As an alternative to a circumferential annular shape of screening plate300, it is also possible to select only a ring-segment form which coversonly the relevant effective area.

A system illustrated in FIGS. 5 a to 6 c is described in the followingas an exemplary embodiment in which the force-transmission element ofdrive gear 100 is a groove 101 aligned along a spiral line. Balls 208,which are stored in a ball cage 201 of output gear 200, engage with thisgroove 101. As illustrated in FIG. 6 b, ball cage 201 is arranged suchthat, on the one hand, balls 208 are able to rotate freely therein aboutall axes and are axially secured against falling out, on the other hand.In the illustrated example, ball cage 201 or entire output gear 200 ismade of plastic, so that balls 208 may be installed in ball cage 201 bysnapping into place.

As illustrated in FIG. 6 a, output gear 200 has sixteen balls 208, whichinteract with a groove 101 (single-gear spiral). On the basis of thisinformation the reduction ratio of 16:1 may be determined.

In this exemplary embodiment, axis of rotation 103 of drive gear 100 istilted with respect to axis of rotation 203 of output gear 200 in theassembled state. In contrast to the exemplary embodiments illustratingcontactless force transmission, there are friction losses and wear inthis example of a contacting force-transmission device. These effectsmay be reduced by lubricating the gearing and by using suitable materialpairings. Wear may be reduced in that the rolling partners, e.g., groove101, balls 208 and ball cage 201, are provided with a wear-reducinghard-material coating such as a tungsten-carbide layer in combinationwith slideable plastics, such coating being applied to all or some ofthe mentioned components. Ball cage 201 may be manufactured fromsintered metal with incorporated lubricants. As an alternative, balls208 and/or the other rolling partner may be made of a ceramic material.

As illustrated in FIG. 7, the gearing is installed in a multiturn rotaryencoder 400 for ascertaining the absolute angular position. Via itslarge central bore, drive gear 100 of the gearing is connected to ahollow shaft 401 of rotary encoder 400 in a rotatably fixed manner.Hollow shaft 401 holds a shaft in a rotatably fixed manner, therotational position of which is to be measured during operation ofrotary encoder 400. Mounted at a shoulder of hollow shaft 401 is a codedisk 402, which is bonded in this example, so that during measuringoperation code disk 402 rotates with the same frequency as hollow shaft401. To record the absolute position within one rotation of hollow shaft401, code disk 402 carries a multi-track code, e.g., a Gray code, thefinest track being a high-resolution incremental track which may bepositioned as far as possible outside at the periphery of code disk 402,to permit the arrangement of as many graduation periods as possible overthe periphery. The more graduation periods are disposed across theentire circumference, the higher the angular resolution of the rotaryencoder to be detected.

Positioned in non-rotating housing 410 of rotary encoder 400 are a lightsource 411, a lens 412 and a scanning plate 413. Furthermore, a wafer414 on the underside of which photodetectors are affixed, is joined tohousing 410 in a rotatably fixed manner. With the aid of this opticalangle scanner the individual angular position within one rotation ofhollow shaft 410 is determined in an incremental and/or absolute manner.

A multiturn measurement may require the gearing and the additional gearsteps cooperating therewith. These are integrated in a gear box 420, theouter wall of which is partially omitted in FIG. 7 for clarity. Gear box420 is joined to housing 410 in a rotatably fixed manner and thus doesnot participate in the rotary motion of hollow shaft 401 or drive gear100. In contrast, axis of rotation 203 of output gear 200 is immoveablealso with respect to gear box 420 and thus with respect to housing 410.Drive gear 100, in a slip-free manner and at the given reduction,transmits the rotary motion of hollow shaft 401 to output gear 200,which is supported in bearing P so as to allow rotation about axis ofrotation 203 relative to gear box 420. A gear wheel, which meshes with agear wheel of an additional reduction step, is connected to output gear200 in a rotatably fixed manner. Mounted on the shaft of this additionalreduction step is a graduated disk 421 having magnetic graduation.Furthermore, additional gear steps having further graduated disks 422and 423 are arranged accordingly. The axes of rotation of graduateddisks 421, 422, 423 are aligned in parallel with hollow shaft 401. Eachgraduated disk 421, 422, 423 is made up of a magnetic body havingmagnetic poles (north, south) arranged by turns in the circumferentialdirection. In the simplest case, graduated disks 421, 422, 423 each takethe form of short bar magnets having a single north pole and south pole.The magnetic graduations of graduated disks 421, 422, 423 are arrangedin a common plane.

In this example, graduated disk 421 rotates more slowly than hollowshaft 401 by a factor of 16, the additional gear steps leading to afurther reduction of the rotational frequencies of correspondinggraduated disks 422, 423.

Via detector devices at the upper side of wafer 414, which are Hallsensors in this case, the angular positions of graduated disks 421, 422,423 are determined. Graduated disks 421, 422, 423 thus measure thenumber of rotations of hollow shaft 401, each graduated disk 421, 422,423 being driven in a geared-down manner via the reduction gear by theparticular gear step connected upstream. For a space-saving design,graduated disks 421, 422, 423 as well as pivot bearing P of axis ofrotation 203 of output gear 200 are arranged within the peripheralregion of code disk 402.

Instead of Hall sensors, it is also possible to use magneto-resistivesensors such as AMR, GMR (giant magneto-resistive) or TMR sensors(tunnel magneto-resistive), etc., as detector devices.

Output gear 200 is installed between drive gear 100 and wafer 414 in thedescribed example. Because of this configuration and due to the factthat the magnetic graduations of graduated disks 421, 422, 423 arearranged in one plane, it may be relatively easy to accommodate theassociated detector devices on the upper face of wafer 414. As describedabove, the corresponding photodetectors are affixed to the underside ofwafer 414. Both sides of wafer 414 may be fitted with electroniccomponents, which may provide certain advantages with respect to therequired space and also the production economy.

The components of the optical scanner (e.g., light source 411, lens 412,sampling plate 413 and code disk 402) are thus situated underneath wafer414 in rotary encoder 400 illustrated in FIG. 7, the photoelements beingaffixed to the underside of wafer 414. Mounted on the upper face ofwafer 414 are, among others, the detector devices for recording therotational positions of graduated disks 421, 422, 423. As illustrated inFIG. 7, the gearing and the additional gear steps are mounted above thewafer. Output gear 200, which similar to drive gear 100 is part of thenovel gearing, does not project beyond the outer diameter of housing410. In this case, it is possible to use a housing 410 of a conventionalrotary encoder since, compared to earlier gearings, the gearing may notenlarge the radial dimensions of rotary encoder 400. Disposed aboveoutput gear 200 is drive gear 100 of the gearing, which is dimensionedsuch that its diameter is not greater than that of housing 410. Due tothe described arrangement, it is therefore possible to produce a rotaryencoder 400 which may have exceedingly small structural dimensions bothin the radial and the axial direction and may be equipped with a gearingthat may have the already described advantages.

As mentioned previously, it may be provided in the describedconfiguration that output gear 200 is arranged such that it does notproject, or projects to only a negligible degree, beyond the outerdiameter of body 106 of drive gear 100. In other words, the clearancebetween bearing P and axis of rotation 103 of the drive gear is notgreater than one-half of the outer diameter of body 106 of drive gear100. In the example illustrated, the clearance between bearing P andaxis of rotation 103 of the drive gear is also not greater than one-halfof the outer diameter of code disk 402. In the event that two or morebearings P are provided in which axis of rotation 203 of output gear 200is supported, the particular bearing P having the shortest clearancewith respect to axis of rotation 103 may be considered in thisexamination, provided axis of rotation 203 of output gear 200 isarranged in a correspondingly inclined manner with respect to axis ofrotation 103 of drive gear 100. As a result of satisfying thesecriteria, the arrangement of the rotary encoders may have a relativelysmall diameter.

The use of the gearing is not limited to rotary encoders whoseincremental scanning is based on an optical principle or whose countingof rotations is based on a magnetic scanning principle. It also covers,among others, rotary encoders having a capacitive or an inductiveeffect.

1-18. (canceled)
 19. A gearing, comprising: a rotatable drive element; arotatable output element; at least one first force-transmission devicearranged at an end face of the drive element along at least one spiralline; and a second force-transmission device arranged at an end face ofthe output element along a circumferential line; wherein in accordancewith reciprocal action of the first force-transmission device and thesecond force-transmission device, the first force-transmission deviceand the second force-transmission device are configured to transmittorque from the drive element to the output element to effect a rotarymotion in the output element, a frequency of rotation of the outputelement lower than a frequency of rotation of the drive element.
 20. Thegearing according to claim 19, wherein the spiral line satisfies thecondition r=a·φ, r representing a radius of the spiral line, arepresenting a constant positive number, and φ representing a pivotingangle of a radial beam originating from a pole of the spiral line. 21.The gearing according to claim 19, wherein a number of the secondforce-transmission device of the output element is greater than aneffective number of threads of the spiral line of the drive element. 22.The gearing according to claim 19, wherein a greatest distance betweenan axis of rotation of the output element and an outer contour of thesecond force-transmission device of the output element is smaller than adistance between axes of rotation of the drive element and the outputelement in a region of the output element.
 23. The gearing according toclaim 19, wherein at least one of (a) the first force-transmissiondevice and (b) the second force-transmission device includes a permanentmagnet.
 24. The gearing according to claim 23, wherein theforce-transmission devices are configured to transmit the torque in acontactless manner.
 25. The gearing according to claim 23, wherein theforce-transmission devices are configured to transmit the torque in acontactless manner by repelling magnetic forces.
 26. The gearingaccording to claim 23, wherein the permanent magnets are arranged on acarrier body, a material of the carrier body having a relativepermeability greater than
 10. 27. The gearing according to claim 23,wherein the permanent magnets are arranged on a carrier body, a materialof the carrier body having a relative permeability greater than
 100. 28.The gearing according to claim 23, wherein at least one permanent magnetof the drive element includes a layer on a side facing the outputelement, the layer including a material having ferromagnetic properties.29. The gearing according to claim 23, wherein permanent magnets of thedrive element are arranged on a plurality of spiral lines and havedifferent bar heights.
 30. The gearing according to claim 23, furthercomprising a third force-transmission device configured to transmittorque in a contacting manner from the drive element to the outputelement.
 31. The gearing according to claim 23, further comprising athird force-transmission device at the output element configured totransmit torque in a contacting manner from the drive element to theoutput element.
 32. The gearing according to claim 30, wherein the thirdforce-transmission device is configured to transmit torque in both thecontacting manner and a non-contacting manner from the drive element tothe output element.
 33. The gearing according to claim 23, wherein amagnetically screened partial region and a non-screened partial regionare located in a region between the drive element and the outputelement.
 34. The gearing according to claim 33, wherein the magneticallyscreened partial region includes a ferromagnet, and the non-screenedpartial region includes a window in the ferromagnet.
 35. The gearingaccording to claim 33, wherein the magnetically screened partial regionincludes a soft magnetic plate, and the non-screened partial regionincludes a window in the plate.
 36. The gearing according to claim 19,wherein the first force-transmission device of the drive elementincludes a groove, and the second force-transmission device of theoutput element includes recesses in which ball elements are arranged.37. The gearing according to claim 19, wherein the secondforce-transmission device includes a plurality of permanent magnetsarranged along the circumferential line, each permanent magnet having apolarity opposite to a polarity of adjacent permanent magnets, at leasta portion of each permanent magnet having a height from the end face ofthe output element different than a height of at least a portion ofadjacent permanent magnets.
 38. A rotary encoder, comprising: at leastone gear step, each gear step including: a rotatable drive element; arotatable output element; at least one first force-transmission devicearranged at an end face of the drive element along at least one spiralline; and a second force-transmission device arranged at an end face ofthe output element along a circumferential line; wherein in accordancewith reciprocal action of the first force-transmission device and thesecond force-transmission device, the first transmission device and thesecond transmission device are configured to transmit torque from thedrive element to the output element to effect a rotary motion in theoutput element, a frequency of rotation of the output element lower thana frequency of rotation of the drive element.
 39. The rotary encoderaccording to claim 38, wherein the output element is arranged betweenthe drive element and a wafer.
 40. The rotary encoder according to claim38, wherein a shortest distance between an axis of rotation of the driveelement and a point at which the output element is supported is notgreater than one-half of a diameter of a body of the drive gear.
 41. Therotary encoder according to claim 38, wherein a shortest distancebetween an axis of rotation of the drive element and a point at whichthe output element is supported is not greater than one-half of adiameter of a code disk.
 42. The rotary encoder according to claim 38,wherein the second force-transmission device includes a plurality ofpermanent magnets arranged along the circumferential line, eachpermanent magnet having a polarity opposite to a polarity of adjacentpermanent magnets, at least a portion of each permanent magnet having aheight from the end face of the output element different than at least aportion of adjacent permanent magnets.
 43. A gearing, comprising:rotatable drive means; rotatable output means; at least one firstforce-transmission means arranged at an end face of the drive meansalong at least one spiral line; and second force-transmission meansarranged at an end face of the output means along a circumferentialline; wherein in accordance with reciprocal action of the firstforce-transmission means and the second force-transmission means, thefirst force-transmission means and the second force-transmission meanstransmit torque from the drive means to the output means to effect arotary motion in the output means, a frequency of rotation of the outputmeans lower than a frequency of rotation of the drive means.
 44. Arotary encoder, comprising: at least one gear step, each gear stepincluding: rotatable drive means; rotatable output means; at least onefirst force-transmission means arranged at an end face of the drivemeans along at least one spiral line; and second force-transmissionmeans arranged at an end face of the output means along acircumferential line; wherein in accordance with reciprocal action ofthe first force-transmission means and the second force-transmissionmeans, the first force-transmission means and the secondforce-transmission means transmit torque from the drive means to theoutput means to effect a rotary motion in the output means, a frequencyof rotation of the output means lower than a frequency of rotation ofthe drive means.